Chromosome level assembly of wild spinach provides insights into the divergence of homo- and heteromorphic plant sex-chromosomes

Abstract

AbstractBackgroundCultivated spinach (Spinacia oleracea)is a highly nutritional crop species of great economical value that belongs to a genus of dioecious plant species with both homomorphic and heteromorphic sex chromosomes. The wild spinach speciesSpinacia turkestanicaandSpinacia tetrandraare important genetic sources for improving cultivated spinach and excellent material for studying sex chromosome evolution in plants. However, until now there were no publicly available genome assemblies for these species.ResultsHere we sequenced and assembled the genomes ofS. turkestanicaandS. tetrandraand performed a tri-way comparative analysis withS. oleracea. We show that many abiotic- and biotic stress related gene clusters have expanded through tandem duplication inS. tetrandraafter it diverged from theS. turkestanica-S. oleracealineage. Focussing on the sex chromosomes we found that the previously identified inversion distinguishing theS. oleraceamale- and female-SEX DETERMINING REGIONs (SDRs) is conserved inS. turkestanica. Although, the SDRs of these two species coincides with the PSEUDO AUTOSOMAL REGION ofS. tetrandrathe gene content is only partially conserved and the genetic factors determining sex in these species might differ. Finally, we show that recombination suppression between theS. tetrandraX- and Y-chromosomes resulted in a highly degenerated Y-chromosome and started before the species diverged fromS. turkestanicaandS. oleracea.ConclusionsWe expect that the novel wild spinach species genomes are of great value to the breeding community and evolutionary biologist especially focussing on the evolution of sex chromosomes in plants.